Personal wash compositions seek to provide consumers additional skin conditioning benefits beyond simple cleansing. The principal benefits provided by such compositions are mildness and moisturization. Because of their low cost, smooth sensory feel, and mildness to skin, emollient oils such as triglyceride based vegetable oils (e.g., soybean oil, sunflower seed oil) and fatty acids are among the most commonly used skin benefit agents.
Emollient oils such as triglycerides and long chain fatty acids can deposit or penetrate into skin from personal wash application to retard skin dehydration and alleviate skin irritation (skin lipid/protein damage) from surfactants. The emollient oils play these roles in body wash products because of their intrinsic water insoluble property (hydrophobicity). However, the oil phase in liquid cleansing formulations may increase the challenge to formulate stable liquid cleansing products because of the inherent incompatibility between aqueous continuous phase and the water immiscible oil phase. High levels of surfactants and/or emulsifiers are frequently used to stabilize the interface between aqueous phase and oil phase to help stabilize the formulations.
A problem in the art is how to provide long term stability over a wide range of transportation/storage temperatures. Surfactant based liquid cleanser formulations use different structuring technologies to form stable formulations. Simple isotropic formulations, for example, can be stabilized using high concentration of surfactant. More complex liquid cleansing formulations, which may contain substantial amounts of skin beneficial agents, use other structuring agents such as suspending polymer, fibers, starch, or solid long chain (>C12) fatty acids to help stabilize the formulations. In order to form a stable and consistent body wash product, usually the composition needs to be formulated at a temperature higher than the melting point of all ingredients in the compositions so that the highest melting solid ingredient can evenly distribute into the surfactant phase. When the temperature decreases below their melting point, however, the contained solid ingredients generally crystallize. Often, small crystal particles grow and precipitate out from the surfactant phase. This can cause both product phase separation and significant viscosity drop. Where the temperature is even lower than the Krafft point of the surfactant phase, co-crystallization of solid fatty acid and surfactant may occur when using solid hydrophobic ingredients.
In applicants' copending U.S. Ser. No. 12/371,050, filed in February 2009, there is disclosed a method of using fully hydrogenated triglyceride oil as a structuring agent to modify the rheology of liquid triglyceride oils. It was found that, within specifically defined ratios of hydrogenated triglycerides to liquid oils, an oil mixture of regular liquid vegetable oils and its hydrogenated derivatives could match the shear thinning property of petrolatum gel and have a negligible impact on the foaming property of liquid cleansing formulations. The IV of the blend is well above that of the saturated triglyceride of the subject invention, which suggests that there is not sufficient saturated triglyceride in the blend to obtain at least 70% viscosity of the original composition. There is further no recognized benefit (e.g., the stability) of our oils, e.g., based on sufficient level of hydrogenated triglyceride to provide required solidness. In a preferred embodiment of our invention, only saturated (hydrogenated) triglycerides are applied or, if used in mixture with other oils, 40% or more, preferably 50% or more of mix comprises saturated triglycerides.
Unexpectedly, applicants have now found that minimum amounts of hydrogenated triglyceride oils (introduced as pure sample or as mixtures with oil where preferably, >40%, more preferably 50% or more of mix is saturated) can stabilize the oil/water interface of liquid products containing fatty acid and thus stabilize the liquid cleansing formulations over a wide range of storage temperature, even temperatures as low as 4° C.
The present invention discloses liquid cleansing compositions comprising critical amounts (0.1-5% by wt.) of hydrogenated triglyceride of defined value to stabilize the compositions over a temperature range of 4° C. to 50° C. The solid hydrogenated triglycerides can be directly added into the surfactant base or be pre-mixed with other hydrophobic oils such as triglyceride oil or hydrocarbon oils (where they preferably comprise 40% or more of the mix sufficient to ensure desired crystallinity for stability). It is critical, however, that total amounts of hydrogenated glycerides in the final composition, regardless of source, be within specific amount range to ensure retention of viscosity after cold temperature storage (4° C. for one week). Use of such minimum amounts of saturated triglyceride (defined by IV 0 to less than 20) in liquid cleansing compositions, preferably in compositions comprising fatty acyl isethionate and amphoteric; or comprising acyl isethionate and alkanoyl glycinate is believed unknown.
In general, triglycerides are the main constituents of vegetable oils and animal fats. A triglyceride, also called triacylglycerol (TAG), is a chemical compound formed from one molecule of glycerol and three fatty acids. Hydrogenated triglycerides are the triglyceride oils produced after the contained unsaturated C═C double bonds are hydrogenated and converted into C—C single bonds. The schematic chemical structure of hydrogenated triglycerides is given below:

where R1, R2, R3 are saturated carboxylic acids which are esterified with glycerol to form saturated triacylglycerol (TAG) esters. The fatty acids in TAG commonly have chain lengths from 10-24, mostly including C10 (Capric acid), C12 (Lauric acid), C14 (Myristic acid), C16 (Palmitic acid), C18 (Stearic acid) and C20 (Arachidic acid) fatty acid. Naturally sourced vegetable oils and fats also contain substantial amount of monounsaturates such as C16:1 (Palmitoleic acid), C18:1 (Oleic acid) and polyunsaturated fatty acids such as C18:2 (Linoleic acid)) and C18:3 (Linolenic acid) and so on, depending on the source of oils and regions. In the oil and grease industry, the hydrogenated triglycerides are synthesized by catalyst induced addition reaction with hydrogen to remove the C═C double bonds in fatty acid chains. The degree of saturation in triglycerides can be quantified by the amount of contained C═C double bonds in the molecule. Conveniently, the Iodine Value (or “iodine adsorption value” or “IV number” or “iodine index”) is often used in lipid chemistry, and is defined as the mass of iodine in grams that is consumed by 100 grams of a chemical substance. For triglycerides, a higher iodine value indicates more unsaturated double bonds in fatty acids. In an ideal case, a fully hydrogenated triglyceride should have Iodine value close to zero as it can not be further reacted with hydrogen. Also, by the definition of Iodine Value, this should be the case for all types of triglyceride oils.
Besides Iodine Value, the solid content (crystal percentage) is another frequently used parameter used to characterize hydrogenated triglycerides, whether added alone or as mixture. Thermal transition analysis (Differential Scanning calorimetry, DSC) is used to measure the contained crystal content by calculating the energy (enthalpy) needed to achieve phase transition of samples (melting for crystal phase or freezing for liquid phase). In DSC, the crystal percentage is calculated by the integrated melting (or freezing) peak of samples as compared to the fully hydrogenated samples of the same oils. At room temperature, the hydrogenated triglyceride (usually have melting point much higher than room temperature), would have 100% crystal percentage while liquid oils have 0% crystal percentage. Oil mixtures have a value somewhere in between.
There has been much work relating to use of hydrogenated triglycerides and structured oils in personal product composition. Some of the most relevant works are briefly listed as following:
EP 1,479,365 discloses benefit agent materials structured with crystalline material. U.S. Publication 2004/023569 A1 discloses non-bar compositions comprising crystalline wax structured benefit agent. U.S. 2004/0234467 A1 discloses compositions comprising structured benefit agent for deposition of hydrophilic benefit agent. EP 1,479,378 relates to bars with crystalline wax structured delivery vehicle.
U.S. 2004/0234468, U.S. 2004/0234469 and U.S. 2004/0234558 disclose structured premix to enhance delivery of hydrophobic agent.
WO 2004/017745 discloses mixing non-hydrogenated and hydrogenated oils for dispersed liquid oil or solid particles in fat phase for food compositions.
None of these references disclose compositions wherein specific critical amounts of hydrogenated triglyceride (delivered, preferably, as pure triglyceride, but also can be delivered as mixture with oils) are used in combination with defined fatty acids to stabilize liquid compositions, preferably those comprising a DEFI surfactant and amphoteric surfactant system, or DEFI surfactant and alkanoyl glycinate surfactant system, over low temperature storage conditions.
U.S. 2005/0281851 to Cap discloses cosmetic products (no liquid cleansing application) comprising vegetable oil blends and additional fatty acid where blends have iodine value range of 20-80, and where no applicable viscosity range is specified. There is no disclosure of use of 0.1-5% of fully hydrogenated triglyceride having IV 0 to <20 or of advantageous use for low temperature stability.
Unexpectedly, applicants have found that when specific range of hydrogenated triglyceride is used in liquid compositions comprising C10-C20 linear fatty acids, low temperature stability (as low as 4° C. for one week) is retained (>70% viscosity, preferably 75% or greater).